The present invention relates to testing for occult gastrointestinal bleeding. The common screening test for occult gastrointestinal bleeding is the test for fecal occult blood (FOB). This test involves placing a sample of stool onto a testing surface and adding one or more reagents which react with the blood in the sample to produce a recognizable color.
Two current varieties of such tests are the Hemoccult.RTM. device and the HemaWipe.RTM. device. The Hemoccult.RTM. test device requires that one use a small paddle to fish a feces sample out of the toilet and apply the sample to a piece of test paper mounted on a card. U.S. Pat. No. 3,996,006 to Pagano is exemplary of a Hemoccult.RTM. test device.
The HemaWipe.RTM. device utilizes a test pad adhered to a pliant impermeable base sheet and covered with a pliant volume control sheet having openings therein in alignment with the test pad. The patient can wipe with the HemaWipe.RTM. device, remove the volume control cover sheet, fold the pliant base sheet over on itself to seal the test pad and sample and submit it for testing. A number of prior patents relate to the HemaWipe.RTM. device including U.S. Pat. No. 4,808,379, entitled "DEVICE FOR OBTAINING STOOL SAMPLES," issued Feb. 18, 1989, U.S. Pat. No. 4,804,518, entitled "DEVICE FOR OCCULT BLOOD TESTING," issued Feb. 14, 1989, U.S. Pat. No. 4,559,949, entitled "STOOL SAMPLING DEVICE," issued Dec. 24, 1985, U.S. Pat. No. 4,420,353, entitled "METHOD OF MAKING A STOOL SAMPLING DEVICE," filed Dec. 13, 1983, U.S. Pat. No. 4,367,750, entitled "DEVICE FOR OBTAINING STOOL SAMPLES," issued Jan. 11, 1983, U.S. Pat. No. 4,273,741, entitled "DEVICE FOR OBTAINING STOOL SAMPLES," issued Jun. 16, 1981, and U.S. Pat. No. 4,259,964, entitled "DEVICE FOR OBTAINING STOOL SAMPLES," issued Apr. 7, 1981.
Virtually all FOB tests used today have the problem of nonspecificity. Their chemical reactions detect the peroxidase property of hemoglobin by causing the catalysis of peroxide into oxygen and water, and the subsequent oxidation of a colorless dye into a colored form. Gum guaiac is the most commonly used color reagent, although a large number of other reagents have been used in the past.
The nonspecificity is due to two reasons. First, there are other peroxidase positive materials which the patient may eat, which, when excreted, will also cause a positive reaction. Secondly, there is a normal, small loss of blood into the GI tract which in some patients will escape into the stool in amounts large enough to cause a reaction. It is obvious that the more sensitive the reagent, the more sensitive the test, but the more likely that there will be a false-positive reaction.
The FOB tests are more frequently used to screen patients for a hidden colonic malignancy, so that the consequences of missing any bleeding can be severe. Conversely, if there are a large number of false-positive tests, the expense and possible complications of the additional follow-up tests involved are also considerable. There have been many attempts to make the FOB test more specific, and thus allow adequate sensitivity while preventing the undesired false-positive results.
Specific immunologic tests have been employed which are sensitive only to human blood. The problem with these have been that they are much more complicated and expensive than the usual screening test, and the blood may be altered by partial digestion so that it is not detected by immunologic means. A recent technique called Hemaquant involves the extraction of a stool sample to obtain porphyrins, the breakdown products of blood. The advantage of this technique is that it is quantitative and relatively specific, but it too is expensive and much more cumbersome than the usual screening tests.
An important consideration in any work-up for GI bleeding is the source. Where the FOB test is used to screen for colo-rectal cancer, the only blood of interest is from the lower GI tract. Blood from gastritis or dental bleeding would be considered a false-positive, even though blood was indeed present. It can therefore be seen that the concept of a false-positive test involves more than the incorrect detection of blood but also the circumstances under which it is detected. Ideally, an FOB test would not only reliably detect blood but also give some indication as to the origin of the blood.
It is therefore an object of this invention to provide a simple but accurate means of detecting a small amount of blood in a sample of stool. It is also a object of this invention to provide an indication of the origin of the blood.